Adjust to reflect 8.0-RELEASE.

[FreeBSD/releng/8.0.git] / sys / vm / swap_pager.c

/*-
 * Copyright (c) 1998 Matthew Dillon,
 * Copyright (c) 1994 John S. Dyson
 * Copyright (c) 1990 University of Utah.
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * the Systems Programming Group of the University of Utah Computer
 * Science Department.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *                              New Swap System
 *                              Matthew Dillon
 *
 * Radix Bitmap 'blists'.
 *
 *      - The new swapper uses the new radix bitmap code.  This should scale
 *        to arbitrarily small or arbitrarily large swap spaces and an almost
 *        arbitrary degree of fragmentation.
 *
 * Features:
 *
 *      - on the fly reallocation of swap during putpages.  The new system
 *        does not try to keep previously allocated swap blocks for dirty
 *        pages.  
 *
 *      - on the fly deallocation of swap
 *
 *      - No more garbage collection required.  Unnecessarily allocated swap
 *        blocks only exist for dirty vm_page_t's now and these are already
 *        cycled (in a high-load system) by the pager.  We also do on-the-fly
 *        removal of invalidated swap blocks when a page is destroyed
 *        or renamed.
 *
 * from: Utah $Hdr: swap_pager.c 1.4 91/04/30$
 *
 *      @(#)swap_pager.c        8.9 (Berkeley) 3/21/94
 *      @(#)vm_swap.c   8.5 (Berkeley) 2/17/94
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_swap.h"
#include "opt_vm.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/conf.h>
#include <sys/kernel.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/bio.h>
#include <sys/buf.h>
#include <sys/disk.h>
#include <sys/fcntl.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/vnode.h>
#include <sys/malloc.h>
#include <sys/resource.h>
#include <sys/resourcevar.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/blist.h>
#include <sys/lock.h>
#include <sys/sx.h>
#include <sys/vmmeter.h>

#include <security/mac/mac_framework.h>

#include <vm/vm.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pager.h>
#include <vm/vm_pageout.h>
#include <vm/vm_param.h>
#include <vm/swap_pager.h>
#include <vm/vm_extern.h>
#include <vm/uma.h>

#include <geom/geom.h>

/*
 * SWB_NPAGES must be a power of 2.  It may be set to 1, 2, 4, 8, or 16
 * pages per allocation.  We recommend you stick with the default of 8.
 * The 16-page limit is due to the radix code (kern/subr_blist.c).
 */
#ifndef MAX_PAGEOUT_CLUSTER
#define MAX_PAGEOUT_CLUSTER 16
#endif

#if !defined(SWB_NPAGES)
#define SWB_NPAGES      MAX_PAGEOUT_CLUSTER
#endif

/*
 * Piecemeal swap metadata structure.  Swap is stored in a radix tree.
 *
 * If SWB_NPAGES is 8 and sizeof(char *) == sizeof(daddr_t), our radix
 * is basically 8.  Assuming PAGE_SIZE == 4096, one tree level represents
 * 32K worth of data, two levels represent 256K, three levels represent
 * 2 MBytes.   This is acceptable.
 *
 * Overall memory utilization is about the same as the old swap structure.
 */
#define SWCORRECT(n) (sizeof(void *) * (n) / sizeof(daddr_t))
#define SWAP_META_PAGES         (SWB_NPAGES * 2)
#define SWAP_META_MASK          (SWAP_META_PAGES - 1)

struct swblock {
        struct swblock  *swb_hnext;
        vm_object_t     swb_object;
        vm_pindex_t     swb_index;
        int             swb_count;
        daddr_t         swb_pages[SWAP_META_PAGES];
};

static struct mtx sw_dev_mtx;
static TAILQ_HEAD(, swdevt) swtailq = TAILQ_HEAD_INITIALIZER(swtailq);
static struct swdevt *swdevhd;  /* Allocate from here next */
static int nswapdev;            /* Number of swap devices */
int swap_pager_avail;
static int swdev_syscall_active = 0; /* serialize swap(on|off) */

static vm_ooffset_t swap_total;
SYSCTL_QUAD(_vm, OID_AUTO, swap_total, CTLFLAG_RD, &swap_total, 0, "");
static vm_ooffset_t swap_reserved;
SYSCTL_QUAD(_vm, OID_AUTO, swap_reserved, CTLFLAG_RD, &swap_reserved, 0, "");
static int overcommit = 0;
SYSCTL_INT(_vm, OID_AUTO, overcommit, CTLFLAG_RW, &overcommit, 0, "");

/* bits from overcommit */
#define SWAP_RESERVE_FORCE_ON           (1 << 0)
#define SWAP_RESERVE_RLIMIT_ON          (1 << 1)
#define SWAP_RESERVE_ALLOW_NONWIRED     (1 << 2)

int
swap_reserve(vm_ooffset_t incr)
{

        return (swap_reserve_by_uid(incr, curthread->td_ucred->cr_ruidinfo));
}

int
swap_reserve_by_uid(vm_ooffset_t incr, struct uidinfo *uip)
{
        vm_ooffset_t r, s;
        int res, error;
        static int curfail;
        static struct timeval lastfail;

        if (incr & PAGE_MASK)
                panic("swap_reserve: & PAGE_MASK");

        res = 0;
        mtx_lock(&sw_dev_mtx);
        r = swap_reserved + incr;
        if (overcommit & SWAP_RESERVE_ALLOW_NONWIRED) {
                s = cnt.v_page_count - cnt.v_free_reserved - cnt.v_wire_count;
                s *= PAGE_SIZE;
        } else
                s = 0;
        s += swap_total;
        if ((overcommit & SWAP_RESERVE_FORCE_ON) == 0 || r <= s ||
            (error = priv_check(curthread, PRIV_VM_SWAP_NOQUOTA)) == 0) {
                res = 1;
                swap_reserved = r;
        }
        mtx_unlock(&sw_dev_mtx);

        if (res) {
                PROC_LOCK(curproc);
                UIDINFO_VMSIZE_LOCK(uip);
                if ((overcommit & SWAP_RESERVE_RLIMIT_ON) != 0 &&
                    uip->ui_vmsize + incr > lim_cur(curproc, RLIMIT_SWAP) &&
                    priv_check(curthread, PRIV_VM_SWAP_NORLIMIT))
                        res = 0;
                else
                        uip->ui_vmsize += incr;
                UIDINFO_VMSIZE_UNLOCK(uip);
                PROC_UNLOCK(curproc);
                if (!res) {
                        mtx_lock(&sw_dev_mtx);
                        swap_reserved -= incr;
                        mtx_unlock(&sw_dev_mtx);
                }
        }
        if (!res && ppsratecheck(&lastfail, &curfail, 1)) {
                printf("uid %d, pid %d: swap reservation for %jd bytes failed\n",
                    curproc->p_pid, uip->ui_uid, incr);
        }

        return (res);
}

void
swap_reserve_force(vm_ooffset_t incr)
{
        struct uidinfo *uip;

        mtx_lock(&sw_dev_mtx);
        swap_reserved += incr;
        mtx_unlock(&sw_dev_mtx);

        uip = curthread->td_ucred->cr_ruidinfo;
        PROC_LOCK(curproc);
        UIDINFO_VMSIZE_LOCK(uip);
        uip->ui_vmsize += incr;
        UIDINFO_VMSIZE_UNLOCK(uip);
        PROC_UNLOCK(curproc);
}

void
swap_release(vm_ooffset_t decr)
{
        struct uidinfo *uip;

        PROC_LOCK(curproc);
        uip = curthread->td_ucred->cr_ruidinfo;
        swap_release_by_uid(decr, uip);
        PROC_UNLOCK(curproc);
}

void
swap_release_by_uid(vm_ooffset_t decr, struct uidinfo *uip)
{

        if (decr & PAGE_MASK)
                panic("swap_release: & PAGE_MASK");

        mtx_lock(&sw_dev_mtx);
        if (swap_reserved < decr)
                panic("swap_reserved < decr");
        swap_reserved -= decr;
        mtx_unlock(&sw_dev_mtx);

        UIDINFO_VMSIZE_LOCK(uip);
        if (uip->ui_vmsize < decr)
                printf("negative vmsize for uid = %d\n", uip->ui_uid);
        uip->ui_vmsize -= decr;
        UIDINFO_VMSIZE_UNLOCK(uip);
}

static void swapdev_strategy(struct buf *, struct swdevt *sw);

#define SWM_FREE        0x02    /* free, period                 */
#define SWM_POP         0x04    /* pop out                      */

int swap_pager_full = 2;        /* swap space exhaustion (task killing) */
static int swap_pager_almost_full = 1; /* swap space exhaustion (w/hysteresis)*/
static int nsw_rcount;          /* free read buffers                    */
static int nsw_wcount_sync;     /* limit write buffers / synchronous    */
static int nsw_wcount_async;    /* limit write buffers / asynchronous   */
static int nsw_wcount_async_max;/* assigned maximum                     */
static int nsw_cluster_max;     /* maximum VOP I/O allowed              */

static struct swblock **swhash;
static int swhash_mask;
static struct mtx swhash_mtx;

static int swap_async_max = 4;  /* maximum in-progress async I/O's      */
static struct sx sw_alloc_sx;


SYSCTL_INT(_vm, OID_AUTO, swap_async_max,
        CTLFLAG_RW, &swap_async_max, 0, "Maximum running async swap ops");

/*
 * "named" and "unnamed" anon region objects.  Try to reduce the overhead
 * of searching a named list by hashing it just a little.
 */

#define NOBJLISTS               8

#define NOBJLIST(handle)        \
        (&swap_pager_object_list[((int)(intptr_t)handle >> 4) & (NOBJLISTS-1)])

static struct mtx sw_alloc_mtx; /* protect list manipulation */ 
static struct pagerlst  swap_pager_object_list[NOBJLISTS];
static uma_zone_t       swap_zone;
static struct vm_object swap_zone_obj;

/*
 * pagerops for OBJT_SWAP - "swap pager".  Some ops are also global procedure
 * calls hooked from other parts of the VM system and do not appear here.
 * (see vm/swap_pager.h).
 */
static vm_object_t
                swap_pager_alloc(void *handle, vm_ooffset_t size,
                    vm_prot_t prot, vm_ooffset_t offset, struct ucred *);
static void     swap_pager_dealloc(vm_object_t object);
static int      swap_pager_getpages(vm_object_t, vm_page_t *, int, int);
static void     swap_pager_putpages(vm_object_t, vm_page_t *, int, boolean_t, int *);
static boolean_t
                swap_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before, int *after);
static void     swap_pager_init(void);
static void     swap_pager_unswapped(vm_page_t);
static void     swap_pager_swapoff(struct swdevt *sp);

struct pagerops swappagerops = {
        .pgo_init =     swap_pager_init,        /* early system initialization of pager */
        .pgo_alloc =    swap_pager_alloc,       /* allocate an OBJT_SWAP object         */
        .pgo_dealloc =  swap_pager_dealloc,     /* deallocate an OBJT_SWAP object       */
        .pgo_getpages = swap_pager_getpages,    /* pagein                               */
        .pgo_putpages = swap_pager_putpages,    /* pageout                              */
        .pgo_haspage =  swap_pager_haspage,     /* get backing store status for page    */
        .pgo_pageunswapped = swap_pager_unswapped,      /* remove swap related to page          */
};

/*
 * dmmax is in page-sized chunks with the new swap system.  It was
 * dev-bsized chunks in the old.  dmmax is always a power of 2.
 *
 * swap_*() routines are externally accessible.  swp_*() routines are
 * internal.
 */
static int dmmax;
static int nswap_lowat = 128;   /* in pages, swap_pager_almost_full warn */
static int nswap_hiwat = 512;   /* in pages, swap_pager_almost_full warn */

SYSCTL_INT(_vm, OID_AUTO, dmmax,
        CTLFLAG_RD, &dmmax, 0, "Maximum size of a swap block");

static void     swp_sizecheck(void);
static void     swp_pager_async_iodone(struct buf *bp);
static int      swapongeom(struct thread *, struct vnode *);
static int      swaponvp(struct thread *, struct vnode *, u_long);
static int      swapoff_one(struct swdevt *sp, struct ucred *cred);

/*
 * Swap bitmap functions
 */
static void     swp_pager_freeswapspace(daddr_t blk, int npages);
static daddr_t  swp_pager_getswapspace(int npages);

/*
 * Metadata functions
 */
static struct swblock **swp_pager_hash(vm_object_t object, vm_pindex_t index);
static void swp_pager_meta_build(vm_object_t, vm_pindex_t, daddr_t);
static void swp_pager_meta_free(vm_object_t, vm_pindex_t, daddr_t);
static void swp_pager_meta_free_all(vm_object_t);
static daddr_t swp_pager_meta_ctl(vm_object_t, vm_pindex_t, int);

/*
 * SWP_SIZECHECK() -    update swap_pager_full indication
 *      
 *      update the swap_pager_almost_full indication and warn when we are
 *      about to run out of swap space, using lowat/hiwat hysteresis.
 *
 *      Clear swap_pager_full ( task killing ) indication when lowat is met.
 *
 *      No restrictions on call
 *      This routine may not block.
 *      This routine must be called at splvm()
 */
static void
swp_sizecheck(void)
{

        if (swap_pager_avail < nswap_lowat) {
                if (swap_pager_almost_full == 0) {
                        printf("swap_pager: out of swap space\n");
                        swap_pager_almost_full = 1;
                }
        } else {
                swap_pager_full = 0;
                if (swap_pager_avail > nswap_hiwat)
                        swap_pager_almost_full = 0;
        }
}

/*
 * SWP_PAGER_HASH() -   hash swap meta data
 *
 *      This is an helper function which hashes the swapblk given
 *      the object and page index.  It returns a pointer to a pointer
 *      to the object, or a pointer to a NULL pointer if it could not
 *      find a swapblk.
 *
 *      This routine must be called at splvm().
 */
static struct swblock **
swp_pager_hash(vm_object_t object, vm_pindex_t index)
{
        struct swblock **pswap;
        struct swblock *swap;

        index &= ~(vm_pindex_t)SWAP_META_MASK;
        pswap = &swhash[(index ^ (int)(intptr_t)object) & swhash_mask];
        while ((swap = *pswap) != NULL) {
                if (swap->swb_object == object &&
                    swap->swb_index == index
                ) {
                        break;
                }
                pswap = &swap->swb_hnext;
        }
        return (pswap);
}

/*
 * SWAP_PAGER_INIT() -  initialize the swap pager!
 *
 *      Expected to be started from system init.  NOTE:  This code is run 
 *      before much else so be careful what you depend on.  Most of the VM
 *      system has yet to be initialized at this point.
 */
static void
swap_pager_init(void)
{
        /*
         * Initialize object lists
         */
        int i;

        for (i = 0; i < NOBJLISTS; ++i)
                TAILQ_INIT(&swap_pager_object_list[i]);
        mtx_init(&sw_alloc_mtx, "swap_pager list", NULL, MTX_DEF);
        mtx_init(&sw_dev_mtx, "swapdev", NULL, MTX_DEF);

        /*
         * Device Stripe, in PAGE_SIZE'd blocks
         */
        dmmax = SWB_NPAGES * 2;
}

/*
 * SWAP_PAGER_SWAP_INIT() - swap pager initialization from pageout process
 *
 *      Expected to be started from pageout process once, prior to entering
 *      its main loop.
 */
void
swap_pager_swap_init(void)
{
        int n, n2;

        /*
         * Number of in-transit swap bp operations.  Don't
         * exhaust the pbufs completely.  Make sure we
         * initialize workable values (0 will work for hysteresis
         * but it isn't very efficient).
         *
         * The nsw_cluster_max is constrained by the bp->b_pages[]
         * array (MAXPHYS/PAGE_SIZE) and our locally defined
         * MAX_PAGEOUT_CLUSTER.   Also be aware that swap ops are
         * constrained by the swap device interleave stripe size.
         *
         * Currently we hardwire nsw_wcount_async to 4.  This limit is 
         * designed to prevent other I/O from having high latencies due to
         * our pageout I/O.  The value 4 works well for one or two active swap
         * devices but is probably a little low if you have more.  Even so,
         * a higher value would probably generate only a limited improvement
         * with three or four active swap devices since the system does not
         * typically have to pageout at extreme bandwidths.   We will want
         * at least 2 per swap devices, and 4 is a pretty good value if you
         * have one NFS swap device due to the command/ack latency over NFS.
         * So it all works out pretty well.
         */
        nsw_cluster_max = min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER);

        mtx_lock(&pbuf_mtx);
        nsw_rcount = (nswbuf + 1) / 2;
        nsw_wcount_sync = (nswbuf + 3) / 4;
        nsw_wcount_async = 4;
        nsw_wcount_async_max = nsw_wcount_async;
        mtx_unlock(&pbuf_mtx);

        /*
         * Initialize our zone.  Right now I'm just guessing on the number
         * we need based on the number of pages in the system.  Each swblock
         * can hold 16 pages, so this is probably overkill.  This reservation
         * is typically limited to around 32MB by default.
         */
        n = cnt.v_page_count / 2;
        if (maxswzone && n > maxswzone / sizeof(struct swblock))
                n = maxswzone / sizeof(struct swblock);
        n2 = n;
        swap_zone = uma_zcreate("SWAPMETA", sizeof(struct swblock), NULL, NULL,
            NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE | UMA_ZONE_VM);
        if (swap_zone == NULL)
                panic("failed to create swap_zone.");
        do {
                if (uma_zone_set_obj(swap_zone, &swap_zone_obj, n))
                        break;
                /*
                 * if the allocation failed, try a zone two thirds the
                 * size of the previous attempt.
                 */
                n -= ((n + 2) / 3);
        } while (n > 0);
        if (n2 != n)
                printf("Swap zone entries reduced from %d to %d.\n", n2, n);
        n2 = n;

        /*
         * Initialize our meta-data hash table.  The swapper does not need to
         * be quite as efficient as the VM system, so we do not use an 
         * oversized hash table.
         *
         *      n:              size of hash table, must be power of 2
         *      swhash_mask:    hash table index mask
         */
        for (n = 1; n < n2 / 8; n *= 2)
                ;
        swhash = malloc(sizeof(struct swblock *) * n, M_VMPGDATA, M_WAITOK | M_ZERO);
        swhash_mask = n - 1;
        mtx_init(&swhash_mtx, "swap_pager swhash", NULL, MTX_DEF);
}

/*
 * SWAP_PAGER_ALLOC() - allocate a new OBJT_SWAP VM object and instantiate
 *                      its metadata structures.
 *
 *      This routine is called from the mmap and fork code to create a new
 *      OBJT_SWAP object.  We do this by creating an OBJT_DEFAULT object
 *      and then converting it with swp_pager_meta_build().
 *
 *      This routine may block in vm_object_allocate() and create a named
 *      object lookup race, so we must interlock.   We must also run at
 *      splvm() for the object lookup to handle races with interrupts, but
 *      we do not have to maintain splvm() in between the lookup and the
 *      add because (I believe) it is not possible to attempt to create
 *      a new swap object w/handle when a default object with that handle
 *      already exists.
 *
 * MPSAFE
 */
static vm_object_t
swap_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
    vm_ooffset_t offset, struct ucred *cred)
{
        vm_object_t object;
        vm_pindex_t pindex;
        struct uidinfo *uip;

        uip = NULL;
        pindex = OFF_TO_IDX(offset + PAGE_MASK + size);
        if (handle) {
                mtx_lock(&Giant);
                /*
                 * Reference existing named region or allocate new one.  There
                 * should not be a race here against swp_pager_meta_build()
                 * as called from vm_page_remove() in regards to the lookup
                 * of the handle.
                 */
                sx_xlock(&sw_alloc_sx);
                object = vm_pager_object_lookup(NOBJLIST(handle), handle);
                if (object == NULL) {
                        if (cred != NULL) {
                                uip = cred->cr_ruidinfo;
                                if (!swap_reserve_by_uid(size, uip)) {
                                        sx_xunlock(&sw_alloc_sx);
                                        mtx_unlock(&Giant);
                                        return (NULL);
                                }
                                uihold(uip);
                        }
                        object = vm_object_allocate(OBJT_DEFAULT, pindex);
                        VM_OBJECT_LOCK(object);
                        object->handle = handle;
                        if (cred != NULL) {
                                object->uip = uip;
                                object->charge = size;
                        }
                        swp_pager_meta_build(object, 0, SWAPBLK_NONE);
                        VM_OBJECT_UNLOCK(object);
                }
                sx_xunlock(&sw_alloc_sx);
                mtx_unlock(&Giant);
        } else {
                if (cred != NULL) {
                        uip = cred->cr_ruidinfo;
                        if (!swap_reserve_by_uid(size, uip))
                                return (NULL);
                        uihold(uip);
                }
                object = vm_object_allocate(OBJT_DEFAULT, pindex);
                VM_OBJECT_LOCK(object);
                if (cred != NULL) {
                        object->uip = uip;
                        object->charge = size;
                }
                swp_pager_meta_build(object, 0, SWAPBLK_NONE);
                VM_OBJECT_UNLOCK(object);
        }
        return (object);
}

/*
 * SWAP_PAGER_DEALLOC() -       remove swap metadata from object
 *
 *      The swap backing for the object is destroyed.  The code is 
 *      designed such that we can reinstantiate it later, but this
 *      routine is typically called only when the entire object is
 *      about to be destroyed.
 *
 *      This routine may block, but no longer does. 
 *
 *      The object must be locked or unreferenceable.
 */
static void
swap_pager_dealloc(vm_object_t object)
{

        /*
         * Remove from list right away so lookups will fail if we block for
         * pageout completion.
         */
        if (object->handle != NULL) {
                mtx_lock(&sw_alloc_mtx);
                TAILQ_REMOVE(NOBJLIST(object->handle), object, pager_object_list);
                mtx_unlock(&sw_alloc_mtx);
        }

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        vm_object_pip_wait(object, "swpdea");

        /*
         * Free all remaining metadata.  We only bother to free it from 
         * the swap meta data.  We do not attempt to free swapblk's still
         * associated with vm_page_t's for this object.  We do not care
         * if paging is still in progress on some objects.
         */
        swp_pager_meta_free_all(object);
}

/************************************************************************
 *                      SWAP PAGER BITMAP ROUTINES                      *
 ************************************************************************/

/*
 * SWP_PAGER_GETSWAPSPACE() -   allocate raw swap space
 *
 *      Allocate swap for the requested number of pages.  The starting
 *      swap block number (a page index) is returned or SWAPBLK_NONE
 *      if the allocation failed.
 *
 *      Also has the side effect of advising that somebody made a mistake
 *      when they configured swap and didn't configure enough.
 *
 *      Must be called at splvm() to avoid races with bitmap frees from
 *      vm_page_remove() aka swap_pager_page_removed().
 *
 *      This routine may not block
 *      This routine must be called at splvm().
 *
 *      We allocate in round-robin fashion from the configured devices.
 */
static daddr_t
swp_pager_getswapspace(int npages)
{
        daddr_t blk;
        struct swdevt *sp;
        int i;

        blk = SWAPBLK_NONE;
        mtx_lock(&sw_dev_mtx);
        sp = swdevhd;
        for (i = 0; i < nswapdev; i++) {
                if (sp == NULL)
                        sp = TAILQ_FIRST(&swtailq);
                if (!(sp->sw_flags & SW_CLOSING)) {
                        blk = blist_alloc(sp->sw_blist, npages);
                        if (blk != SWAPBLK_NONE) {
                                blk += sp->sw_first;
                                sp->sw_used += npages;
                                swap_pager_avail -= npages;
                                swp_sizecheck();
                                swdevhd = TAILQ_NEXT(sp, sw_list);
                                goto done;
                        }
                }
                sp = TAILQ_NEXT(sp, sw_list);
        }
        if (swap_pager_full != 2) {
                printf("swap_pager_getswapspace(%d): failed\n", npages);
                swap_pager_full = 2;
                swap_pager_almost_full = 1;
        }
        swdevhd = NULL;
done:
        mtx_unlock(&sw_dev_mtx);
        return (blk);
}

static int
swp_pager_isondev(daddr_t blk, struct swdevt *sp)
{

        return (blk >= sp->sw_first && blk < sp->sw_end);
}
        
static void
swp_pager_strategy(struct buf *bp)
{
        struct swdevt *sp;

        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(sp, &swtailq, sw_list) {
                if (bp->b_blkno >= sp->sw_first && bp->b_blkno < sp->sw_end) {
                        mtx_unlock(&sw_dev_mtx);
                        sp->sw_strategy(bp, sp);
                        return;
                }
        }
        panic("Swapdev not found");
}
        

/*
 * SWP_PAGER_FREESWAPSPACE() -  free raw swap space 
 *
 *      This routine returns the specified swap blocks back to the bitmap.
 *
 *      Note:  This routine may not block (it could in the old swap code),
 *      and through the use of the new blist routines it does not block.
 *
 *      We must be called at splvm() to avoid races with bitmap frees from
 *      vm_page_remove() aka swap_pager_page_removed().
 *
 *      This routine may not block
 *      This routine must be called at splvm().
 */
static void
swp_pager_freeswapspace(daddr_t blk, int npages)
{
        struct swdevt *sp;

        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(sp, &swtailq, sw_list) {
                if (blk >= sp->sw_first && blk < sp->sw_end) {
                        sp->sw_used -= npages;
                        /*
                         * If we are attempting to stop swapping on
                         * this device, we don't want to mark any
                         * blocks free lest they be reused.  
                         */
                        if ((sp->sw_flags & SW_CLOSING) == 0) {
                                blist_free(sp->sw_blist, blk - sp->sw_first,
                                    npages);
                                swap_pager_avail += npages;
                                swp_sizecheck();
                        }
                        mtx_unlock(&sw_dev_mtx);
                        return;
                }
        }
        panic("Swapdev not found");
}

/*
 * SWAP_PAGER_FREESPACE() -     frees swap blocks associated with a page
 *                              range within an object.
 *
 *      This is a globally accessible routine.
 *
 *      This routine removes swapblk assignments from swap metadata.
 *
 *      The external callers of this routine typically have already destroyed 
 *      or renamed vm_page_t's associated with this range in the object so 
 *      we should be ok.
 *
 *      This routine may be called at any spl.  We up our spl to splvm temporarily
 *      in order to perform the metadata removal.
 */
void
swap_pager_freespace(vm_object_t object, vm_pindex_t start, vm_size_t size)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        swp_pager_meta_free(object, start, size);
}

/*
 * SWAP_PAGER_RESERVE() - reserve swap blocks in object
 *
 *      Assigns swap blocks to the specified range within the object.  The 
 *      swap blocks are not zerod.  Any previous swap assignment is destroyed.
 *
 *      Returns 0 on success, -1 on failure.
 */
int
swap_pager_reserve(vm_object_t object, vm_pindex_t start, vm_size_t size)
{
        int n = 0;
        daddr_t blk = SWAPBLK_NONE;
        vm_pindex_t beg = start;        /* save start index */

        VM_OBJECT_LOCK(object);
        while (size) {
                if (n == 0) {
                        n = BLIST_MAX_ALLOC;
                        while ((blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE) {
                                n >>= 1;
                                if (n == 0) {
                                        swp_pager_meta_free(object, beg, start - beg);
                                        VM_OBJECT_UNLOCK(object);
                                        return (-1);
                                }
                        }
                }
                swp_pager_meta_build(object, start, blk);
                --size;
                ++start;
                ++blk;
                --n;
        }
        swp_pager_meta_free(object, start, n);
        VM_OBJECT_UNLOCK(object);
        return (0);
}

/*
 * SWAP_PAGER_COPY() -  copy blocks from source pager to destination pager
 *                      and destroy the source.
 *
 *      Copy any valid swapblks from the source to the destination.  In
 *      cases where both the source and destination have a valid swapblk,
 *      we keep the destination's.
 *
 *      This routine is allowed to block.  It may block allocating metadata
 *      indirectly through swp_pager_meta_build() or if paging is still in
 *      progress on the source. 
 *
 *      This routine can be called at any spl
 *
 *      XXX vm_page_collapse() kinda expects us not to block because we 
 *      supposedly do not need to allocate memory, but for the moment we
 *      *may* have to get a little memory from the zone allocator, but
 *      it is taken from the interrupt memory.  We should be ok. 
 *
 *      The source object contains no vm_page_t's (which is just as well)
 *
 *      The source object is of type OBJT_SWAP.
 *
 *      The source and destination objects must be locked or 
 *      inaccessible (XXX are they ?)
 */
void
swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
    vm_pindex_t offset, int destroysource)
{
        vm_pindex_t i;

        VM_OBJECT_LOCK_ASSERT(srcobject, MA_OWNED);
        VM_OBJECT_LOCK_ASSERT(dstobject, MA_OWNED);

        /*
         * If destroysource is set, we remove the source object from the 
         * swap_pager internal queue now. 
         */
        if (destroysource) {
                if (srcobject->handle != NULL) {
                        mtx_lock(&sw_alloc_mtx);
                        TAILQ_REMOVE(
                            NOBJLIST(srcobject->handle),
                            srcobject,
                            pager_object_list
                        );
                        mtx_unlock(&sw_alloc_mtx);
                }
        }

        /*
         * transfer source to destination.
         */
        for (i = 0; i < dstobject->size; ++i) {
                daddr_t dstaddr;

                /*
                 * Locate (without changing) the swapblk on the destination,
                 * unless it is invalid in which case free it silently, or
                 * if the destination is a resident page, in which case the
                 * source is thrown away.
                 */
                dstaddr = swp_pager_meta_ctl(dstobject, i, 0);

                if (dstaddr == SWAPBLK_NONE) {
                        /*
                         * Destination has no swapblk and is not resident,
                         * copy source.
                         */
                        daddr_t srcaddr;

                        srcaddr = swp_pager_meta_ctl(
                            srcobject, 
                            i + offset,
                            SWM_POP
                        );

                        if (srcaddr != SWAPBLK_NONE) {
                                /*
                                 * swp_pager_meta_build() can sleep.
                                 */
                                vm_object_pip_add(srcobject, 1);
                                VM_OBJECT_UNLOCK(srcobject);
                                vm_object_pip_add(dstobject, 1);
                                swp_pager_meta_build(dstobject, i, srcaddr);
                                vm_object_pip_wakeup(dstobject);
                                VM_OBJECT_LOCK(srcobject);
                                vm_object_pip_wakeup(srcobject);
                        }
                } else {
                        /*
                         * Destination has valid swapblk or it is represented
                         * by a resident page.  We destroy the sourceblock.
                         */
                        
                        swp_pager_meta_ctl(srcobject, i + offset, SWM_FREE);
                }
        }

        /*
         * Free left over swap blocks in source.
         *
         * We have to revert the type to OBJT_DEFAULT so we do not accidently
         * double-remove the object from the swap queues.
         */
        if (destroysource) {
                swp_pager_meta_free_all(srcobject);
                /*
                 * Reverting the type is not necessary, the caller is going
                 * to destroy srcobject directly, but I'm doing it here
                 * for consistency since we've removed the object from its
                 * queues.
                 */
                srcobject->type = OBJT_DEFAULT;
        }
}

/*
 * SWAP_PAGER_HASPAGE() -       determine if we have good backing store for
 *                              the requested page.
 *
 *      We determine whether good backing store exists for the requested
 *      page and return TRUE if it does, FALSE if it doesn't.
 *
 *      If TRUE, we also try to determine how much valid, contiguous backing
 *      store exists before and after the requested page within a reasonable
 *      distance.  We do not try to restrict it to the swap device stripe
 *      (that is handled in getpages/putpages).  It probably isn't worth
 *      doing here.
 */
static boolean_t
swap_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before, int *after)
{
        daddr_t blk0;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        /*
         * do we have good backing store at the requested index ?
         */
        blk0 = swp_pager_meta_ctl(object, pindex, 0);

        if (blk0 == SWAPBLK_NONE) {
                if (before)
                        *before = 0;
                if (after)
                        *after = 0;
                return (FALSE);
        }

        /*
         * find backwards-looking contiguous good backing store
         */
        if (before != NULL) {
                int i;

                for (i = 1; i < (SWB_NPAGES/2); ++i) {
                        daddr_t blk;

                        if (i > pindex)
                                break;
                        blk = swp_pager_meta_ctl(object, pindex - i, 0);
                        if (blk != blk0 - i)
                                break;
                }
                *before = (i - 1);
        }

        /*
         * find forward-looking contiguous good backing store
         */
        if (after != NULL) {
                int i;

                for (i = 1; i < (SWB_NPAGES/2); ++i) {
                        daddr_t blk;

                        blk = swp_pager_meta_ctl(object, pindex + i, 0);
                        if (blk != blk0 + i)
                                break;
                }
                *after = (i - 1);
        }
        return (TRUE);
}

/*
 * SWAP_PAGER_PAGE_UNSWAPPED() - remove swap backing store related to page
 *
 *      This removes any associated swap backing store, whether valid or
 *      not, from the page.  
 *
 *      This routine is typically called when a page is made dirty, at
 *      which point any associated swap can be freed.  MADV_FREE also
 *      calls us in a special-case situation
 *
 *      NOTE!!!  If the page is clean and the swap was valid, the caller
 *      should make the page dirty before calling this routine.  This routine
 *      does NOT change the m->dirty status of the page.  Also: MADV_FREE
 *      depends on it.
 *
 *      This routine may not block
 *      This routine must be called at splvm()
 */
static void
swap_pager_unswapped(vm_page_t m)
{

        VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
        swp_pager_meta_ctl(m->object, m->pindex, SWM_FREE);
}

/*
 * SWAP_PAGER_GETPAGES() - bring pages in from swap
 *
 *      Attempt to retrieve (m, count) pages from backing store, but make
 *      sure we retrieve at least m[reqpage].  We try to load in as large
 *      a chunk surrounding m[reqpage] as is contiguous in swap and which
 *      belongs to the same object.
 *
 *      The code is designed for asynchronous operation and 
 *      immediate-notification of 'reqpage' but tends not to be
 *      used that way.  Please do not optimize-out this algorithmic
 *      feature, I intend to improve on it in the future.
 *
 *      The parent has a single vm_object_pip_add() reference prior to
 *      calling us and we should return with the same.
 *
 *      The parent has BUSY'd the pages.  We should return with 'm'
 *      left busy, but the others adjusted.
 */
static int
swap_pager_getpages(vm_object_t object, vm_page_t *m, int count, int reqpage)
{
        struct buf *bp;
        vm_page_t mreq;
        int i;
        int j;
        daddr_t blk;

        mreq = m[reqpage];

        KASSERT(mreq->object == object,
            ("swap_pager_getpages: object mismatch %p/%p",
            object, mreq->object));

        /*
         * Calculate range to retrieve.  The pages have already been assigned
         * their swapblks.  We require a *contiguous* range but we know it to
         * not span devices.   If we do not supply it, bad things
         * happen.  Note that blk, iblk & jblk can be SWAPBLK_NONE, but the 
         * loops are set up such that the case(s) are handled implicitly.
         *
         * The swp_*() calls must be made at splvm().  vm_page_free() does
         * not need to be, but it will go a little faster if it is.
         */
        blk = swp_pager_meta_ctl(mreq->object, mreq->pindex, 0);

        for (i = reqpage - 1; i >= 0; --i) {
                daddr_t iblk;

                iblk = swp_pager_meta_ctl(m[i]->object, m[i]->pindex, 0);
                if (blk != iblk + (reqpage - i))
                        break;
        }
        ++i;

        for (j = reqpage + 1; j < count; ++j) {
                daddr_t jblk;

                jblk = swp_pager_meta_ctl(m[j]->object, m[j]->pindex, 0);
                if (blk != jblk - (j - reqpage))
                        break;
        }

        /*
         * free pages outside our collection range.   Note: we never free
         * mreq, it must remain busy throughout.
         */
        if (0 < i || j < count) {
                int k;

                vm_page_lock_queues();
                for (k = 0; k < i; ++k)
                        vm_page_free(m[k]);
                for (k = j; k < count; ++k)
                        vm_page_free(m[k]);
                vm_page_unlock_queues();
        }

        /*
         * Return VM_PAGER_FAIL if we have nothing to do.  Return mreq 
         * still busy, but the others unbusied.
         */
        if (blk == SWAPBLK_NONE)
                return (VM_PAGER_FAIL);

        /*
         * Getpbuf() can sleep.
         */
        VM_OBJECT_UNLOCK(object);
        /*
         * Get a swap buffer header to perform the IO
         */
        bp = getpbuf(&nsw_rcount);
        bp->b_flags |= B_PAGING;

        /*
         * map our page(s) into kva for input
         */
        pmap_qenter((vm_offset_t)bp->b_data, m + i, j - i);

        bp->b_iocmd = BIO_READ;
        bp->b_iodone = swp_pager_async_iodone;
        bp->b_rcred = crhold(thread0.td_ucred);
        bp->b_wcred = crhold(thread0.td_ucred);
        bp->b_blkno = blk - (reqpage - i);
        bp->b_bcount = PAGE_SIZE * (j - i);
        bp->b_bufsize = PAGE_SIZE * (j - i);
        bp->b_pager.pg_reqpage = reqpage - i;

        VM_OBJECT_LOCK(object);
        {
                int k;

                for (k = i; k < j; ++k) {
                        bp->b_pages[k - i] = m[k];
                        m[k]->oflags |= VPO_SWAPINPROG;
                }
        }
        bp->b_npages = j - i;

        PCPU_INC(cnt.v_swapin);
        PCPU_ADD(cnt.v_swappgsin, bp->b_npages);

        /*
         * We still hold the lock on mreq, and our automatic completion routine
         * does not remove it.
         */
        vm_object_pip_add(object, bp->b_npages);
        VM_OBJECT_UNLOCK(object);

        /*
         * perform the I/O.  NOTE!!!  bp cannot be considered valid after
         * this point because we automatically release it on completion.
         * Instead, we look at the one page we are interested in which we
         * still hold a lock on even through the I/O completion.
         *
         * The other pages in our m[] array are also released on completion,
         * so we cannot assume they are valid anymore either.
         *
         * NOTE: b_blkno is destroyed by the call to swapdev_strategy
         */
        BUF_KERNPROC(bp);
        swp_pager_strategy(bp);

        /*
         * wait for the page we want to complete.  VPO_SWAPINPROG is always
         * cleared on completion.  If an I/O error occurs, SWAPBLK_NONE
         * is set in the meta-data.
         */
        VM_OBJECT_LOCK(object);
        while ((mreq->oflags & VPO_SWAPINPROG) != 0) {
                mreq->oflags |= VPO_WANTED;
                vm_page_lock_queues();
                vm_page_flag_set(mreq, PG_REFERENCED);
                vm_page_unlock_queues();
                PCPU_INC(cnt.v_intrans);
                if (msleep(mreq, VM_OBJECT_MTX(object), PSWP, "swread", hz*20)) {
                        printf(
"swap_pager: indefinite wait buffer: bufobj: %p, blkno: %jd, size: %ld\n",
                            bp->b_bufobj, (intmax_t)bp->b_blkno, bp->b_bcount);
                }
        }

        /*
         * mreq is left busied after completion, but all the other pages
         * are freed.  If we had an unrecoverable read error the page will
         * not be valid.
         */
        if (mreq->valid != VM_PAGE_BITS_ALL) {
                return (VM_PAGER_ERROR);
        } else {
                return (VM_PAGER_OK);
        }

        /*
         * A final note: in a low swap situation, we cannot deallocate swap
         * and mark a page dirty here because the caller is likely to mark
         * the page clean when we return, causing the page to possibly revert 
         * to all-zero's later.
         */
}

/*
 *      swap_pager_putpages: 
 *
 *      Assign swap (if necessary) and initiate I/O on the specified pages.
 *
 *      We support both OBJT_DEFAULT and OBJT_SWAP objects.  DEFAULT objects
 *      are automatically converted to SWAP objects.
 *
 *      In a low memory situation we may block in VOP_STRATEGY(), but the new 
 *      vm_page reservation system coupled with properly written VFS devices 
 *      should ensure that no low-memory deadlock occurs.  This is an area
 *      which needs work.
 *
 *      The parent has N vm_object_pip_add() references prior to
 *      calling us and will remove references for rtvals[] that are
 *      not set to VM_PAGER_PEND.  We need to remove the rest on I/O
 *      completion.
 *
 *      The parent has soft-busy'd the pages it passes us and will unbusy
 *      those whos rtvals[] entry is not set to VM_PAGER_PEND on return.
 *      We need to unbusy the rest on I/O completion.
 */
void
swap_pager_putpages(vm_object_t object, vm_page_t *m, int count,
    boolean_t sync, int *rtvals)
{
        int i;
        int n = 0;

        if (count && m[0]->object != object) {
                panic("swap_pager_putpages: object mismatch %p/%p", 
                    object, 
                    m[0]->object
                );
        }

        /*
         * Step 1
         *
         * Turn object into OBJT_SWAP
         * check for bogus sysops
         * force sync if not pageout process
         */
        if (object->type != OBJT_SWAP)
                swp_pager_meta_build(object, 0, SWAPBLK_NONE);
        VM_OBJECT_UNLOCK(object);

        if (curproc != pageproc)
                sync = TRUE;

        /*
         * Step 2
         *
         * Update nsw parameters from swap_async_max sysctl values.  
         * Do not let the sysop crash the machine with bogus numbers.
         */
        mtx_lock(&pbuf_mtx);
        if (swap_async_max != nsw_wcount_async_max) {
                int n;

                /*
                 * limit range
                 */
                if ((n = swap_async_max) > nswbuf / 2)
                        n = nswbuf / 2;
                if (n < 1)
                        n = 1;
                swap_async_max = n;

                /*
                 * Adjust difference ( if possible ).  If the current async
                 * count is too low, we may not be able to make the adjustment
                 * at this time.
                 */
                n -= nsw_wcount_async_max;
                if (nsw_wcount_async + n >= 0) {
                        nsw_wcount_async += n;
                        nsw_wcount_async_max += n;
                        wakeup(&nsw_wcount_async);
                }
        }
        mtx_unlock(&pbuf_mtx);

        /*
         * Step 3
         *
         * Assign swap blocks and issue I/O.  We reallocate swap on the fly.
         * The page is left dirty until the pageout operation completes
         * successfully.
         */
        for (i = 0; i < count; i += n) {
                int j;
                struct buf *bp;
                daddr_t blk;

                /*
                 * Maximum I/O size is limited by a number of factors.
                 */
                n = min(BLIST_MAX_ALLOC, count - i);
                n = min(n, nsw_cluster_max);

                /*
                 * Get biggest block of swap we can.  If we fail, fall
                 * back and try to allocate a smaller block.  Don't go
                 * overboard trying to allocate space if it would overly
                 * fragment swap.
                 */
                while (
                    (blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE &&
                    n > 4
                ) {
                        n >>= 1;
                }
                if (blk == SWAPBLK_NONE) {
                        for (j = 0; j < n; ++j)
                                rtvals[i+j] = VM_PAGER_FAIL;
                        continue;
                }

                /*
                 * All I/O parameters have been satisfied, build the I/O
                 * request and assign the swap space.
                 */
                if (sync == TRUE) {
                        bp = getpbuf(&nsw_wcount_sync);
                } else {
                        bp = getpbuf(&nsw_wcount_async);
                        bp->b_flags = B_ASYNC;
                }
                bp->b_flags |= B_PAGING;
                bp->b_iocmd = BIO_WRITE;

                pmap_qenter((vm_offset_t)bp->b_data, &m[i], n);

                bp->b_rcred = crhold(thread0.td_ucred);
                bp->b_wcred = crhold(thread0.td_ucred);
                bp->b_bcount = PAGE_SIZE * n;
                bp->b_bufsize = PAGE_SIZE * n;
                bp->b_blkno = blk;

                VM_OBJECT_LOCK(object);
                for (j = 0; j < n; ++j) {
                        vm_page_t mreq = m[i+j];

                        swp_pager_meta_build(
                            mreq->object, 
                            mreq->pindex,
                            blk + j
                        );
                        vm_page_dirty(mreq);
                        rtvals[i+j] = VM_PAGER_OK;

                        mreq->oflags |= VPO_SWAPINPROG;
                        bp->b_pages[j] = mreq;
                }
                VM_OBJECT_UNLOCK(object);
                bp->b_npages = n;
                /*
                 * Must set dirty range for NFS to work.
                 */
                bp->b_dirtyoff = 0;
                bp->b_dirtyend = bp->b_bcount;

                PCPU_INC(cnt.v_swapout);
                PCPU_ADD(cnt.v_swappgsout, bp->b_npages);

                /*
                 * asynchronous
                 *
                 * NOTE: b_blkno is destroyed by the call to swapdev_strategy
                 */
                if (sync == FALSE) {
                        bp->b_iodone = swp_pager_async_iodone;
                        BUF_KERNPROC(bp);
                        swp_pager_strategy(bp);

                        for (j = 0; j < n; ++j)
                                rtvals[i+j] = VM_PAGER_PEND;
                        /* restart outter loop */
                        continue;
                }

                /*
                 * synchronous
                 *
                 * NOTE: b_blkno is destroyed by the call to swapdev_strategy
                 */
                bp->b_iodone = bdone;
                swp_pager_strategy(bp);

                /*
                 * Wait for the sync I/O to complete, then update rtvals.
                 * We just set the rtvals[] to VM_PAGER_PEND so we can call
                 * our async completion routine at the end, thus avoiding a
                 * double-free.
                 */
                bwait(bp, PVM, "swwrt");
                for (j = 0; j < n; ++j)
                        rtvals[i+j] = VM_PAGER_PEND;
                /*
                 * Now that we are through with the bp, we can call the
                 * normal async completion, which frees everything up.
                 */
                swp_pager_async_iodone(bp);
        }
        VM_OBJECT_LOCK(object);
}

/*
 *      swp_pager_async_iodone:
 *
 *      Completion routine for asynchronous reads and writes from/to swap.
 *      Also called manually by synchronous code to finish up a bp.
 *
 *      For READ operations, the pages are PG_BUSY'd.  For WRITE operations, 
 *      the pages are vm_page_t->busy'd.  For READ operations, we PG_BUSY 
 *      unbusy all pages except the 'main' request page.  For WRITE 
 *      operations, we vm_page_t->busy'd unbusy all pages ( we can do this 
 *      because we marked them all VM_PAGER_PEND on return from putpages ).
 *
 *      This routine may not block.
 */
static void
swp_pager_async_iodone(struct buf *bp)
{
        int i;
        vm_object_t object = NULL;

        /*
         * report error
         */
        if (bp->b_ioflags & BIO_ERROR) {
                printf(
                    "swap_pager: I/O error - %s failed; blkno %ld,"
                        "size %ld, error %d\n",
                    ((bp->b_iocmd == BIO_READ) ? "pagein" : "pageout"),
                    (long)bp->b_blkno, 
                    (long)bp->b_bcount,
                    bp->b_error
                );
        }

        /*
         * remove the mapping for kernel virtual
         */
        pmap_qremove((vm_offset_t)bp->b_data, bp->b_npages);

        if (bp->b_npages) {
                object = bp->b_pages[0]->object;
                VM_OBJECT_LOCK(object);
        }
        vm_page_lock_queues();
        /*
         * cleanup pages.  If an error occurs writing to swap, we are in
         * very serious trouble.  If it happens to be a disk error, though,
         * we may be able to recover by reassigning the swap later on.  So
         * in this case we remove the m->swapblk assignment for the page 
         * but do not free it in the rlist.  The errornous block(s) are thus
         * never reallocated as swap.  Redirty the page and continue.
         */
        for (i = 0; i < bp->b_npages; ++i) {
                vm_page_t m = bp->b_pages[i];

                m->oflags &= ~VPO_SWAPINPROG;

                if (bp->b_ioflags & BIO_ERROR) {
                        /*
                         * If an error occurs I'd love to throw the swapblk
                         * away without freeing it back to swapspace, so it
                         * can never be used again.  But I can't from an 
                         * interrupt.
                         */
                        if (bp->b_iocmd == BIO_READ) {
                                /*
                                 * When reading, reqpage needs to stay
                                 * locked for the parent, but all other
                                 * pages can be freed.  We still want to
                                 * wakeup the parent waiting on the page,
                                 * though.  ( also: pg_reqpage can be -1 and 
                                 * not match anything ).
                                 *
                                 * We have to wake specifically requested pages
                                 * up too because we cleared VPO_SWAPINPROG and
                                 * someone may be waiting for that.
                                 *
                                 * NOTE: for reads, m->dirty will probably
                                 * be overridden by the original caller of
                                 * getpages so don't play cute tricks here.
                                 */
                                m->valid = 0;
                                if (i != bp->b_pager.pg_reqpage)
                                        vm_page_free(m);
                                else
                                        vm_page_flash(m);
                                /*
                                 * If i == bp->b_pager.pg_reqpage, do not wake 
                                 * the page up.  The caller needs to.
                                 */
                        } else {
                                /*
                                 * If a write error occurs, reactivate page
                                 * so it doesn't clog the inactive list,
                                 * then finish the I/O.
                                 */
                                vm_page_dirty(m);
                                vm_page_activate(m);
                                vm_page_io_finish(m);
                        }
                } else if (bp->b_iocmd == BIO_READ) {
                        /*
                         * NOTE: for reads, m->dirty will probably be 
                         * overridden by the original caller of getpages so
                         * we cannot set them in order to free the underlying
                         * swap in a low-swap situation.  I don't think we'd
                         * want to do that anyway, but it was an optimization
                         * that existed in the old swapper for a time before
                         * it got ripped out due to precisely this problem.
                         *
                         * If not the requested page then deactivate it.
                         *
                         * Note that the requested page, reqpage, is left
                         * busied, but we still have to wake it up.  The
                         * other pages are released (unbusied) by 
                         * vm_page_wakeup().
                         */
                        KASSERT(!pmap_page_is_mapped(m),
                            ("swp_pager_async_iodone: page %p is mapped", m));
                        m->valid = VM_PAGE_BITS_ALL;
                        KASSERT(m->dirty == 0,
                            ("swp_pager_async_iodone: page %p is dirty", m));

                        /*
                         * We have to wake specifically requested pages
                         * up too because we cleared VPO_SWAPINPROG and
                         * could be waiting for it in getpages.  However,
                         * be sure to not unbusy getpages specifically
                         * requested page - getpages expects it to be 
                         * left busy.
                         */
                        if (i != bp->b_pager.pg_reqpage) {
                                vm_page_deactivate(m);
                                vm_page_wakeup(m);
                        } else {
                                vm_page_flash(m);
                        }
                } else {
                        /*
                         * For write success, clear the dirty
                         * status, then finish the I/O ( which decrements the 
                         * busy count and possibly wakes waiter's up ).
                         */
                        KASSERT((m->flags & PG_WRITEABLE) == 0,
                            ("swp_pager_async_iodone: page %p is not write"
                            " protected", m));
                        vm_page_undirty(m);
                        vm_page_io_finish(m);
                        if (vm_page_count_severe())
                                vm_page_try_to_cache(m);
                }
        }
        vm_page_unlock_queues();

        /*
         * adjust pip.  NOTE: the original parent may still have its own
         * pip refs on the object.
         */
        if (object != NULL) {
                vm_object_pip_wakeupn(object, bp->b_npages);
                VM_OBJECT_UNLOCK(object);
        }

        /* 
         * swapdev_strategy() manually sets b_vp and b_bufobj before calling 
         * bstrategy(). Set them back to NULL now we're done with it, or we'll
         * trigger a KASSERT in relpbuf().
         */
        if (bp->b_vp) {
                    bp->b_vp = NULL;
                    bp->b_bufobj = NULL;
        }
        /*
         * release the physical I/O buffer
         */
        relpbuf(
            bp, 
            ((bp->b_iocmd == BIO_READ) ? &nsw_rcount : 
                ((bp->b_flags & B_ASYNC) ? 
                    &nsw_wcount_async : 
                    &nsw_wcount_sync
                )
            )
        );
}

/*
 *      swap_pager_isswapped:
 *
 *      Return 1 if at least one page in the given object is paged
 *      out to the given swap device.
 *
 *      This routine may not block.
 */
int
swap_pager_isswapped(vm_object_t object, struct swdevt *sp)
{
        daddr_t index = 0;
        int bcount;
        int i;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        if (object->type != OBJT_SWAP)
                return (0);

        mtx_lock(&swhash_mtx);
        for (bcount = 0; bcount < object->un_pager.swp.swp_bcount; bcount++) {
                struct swblock *swap;

                if ((swap = *swp_pager_hash(object, index)) != NULL) {
                        for (i = 0; i < SWAP_META_PAGES; ++i) {
                                if (swp_pager_isondev(swap->swb_pages[i], sp)) {
                                        mtx_unlock(&swhash_mtx);
                                        return (1);
                                }
                        }
                }
                index += SWAP_META_PAGES;
                if (index > 0x20000000)
                        panic("swap_pager_isswapped: failed to locate all swap meta blocks");
        }
        mtx_unlock(&swhash_mtx);
        return (0);
}

/*
 * SWP_PAGER_FORCE_PAGEIN() - force a swap block to be paged in
 *
 *      This routine dissociates the page at the given index within a
 *      swap block from its backing store, paging it in if necessary.
 *      If the page is paged in, it is placed in the inactive queue,
 *      since it had its backing store ripped out from under it.
 *      We also attempt to swap in all other pages in the swap block,
 *      we only guarantee that the one at the specified index is
 *      paged in.
 *
 *      XXX - The code to page the whole block in doesn't work, so we
 *            revert to the one-by-one behavior for now.  Sigh.
 */
static inline void
swp_pager_force_pagein(vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t m;

        vm_object_pip_add(object, 1);
        m = vm_page_grab(object, pindex, VM_ALLOC_NORMAL|VM_ALLOC_RETRY);
        if (m->valid == VM_PAGE_BITS_ALL) {
                vm_object_pip_subtract(object, 1);
                vm_page_lock_queues();
                vm_page_activate(m);
                vm_page_dirty(m);
                vm_page_unlock_queues();
                vm_page_wakeup(m);
                vm_pager_page_unswapped(m);
                return;
        }

        if (swap_pager_getpages(object, &m, 1, 0) != VM_PAGER_OK)
                panic("swap_pager_force_pagein: read from swap failed");/*XXX*/
        vm_object_pip_subtract(object, 1);
        vm_page_lock_queues();
        vm_page_dirty(m);
        vm_page_dontneed(m);
        vm_page_unlock_queues();
        vm_page_wakeup(m);
        vm_pager_page_unswapped(m);
}

/*
 *      swap_pager_swapoff:
 *
 *      Page in all of the pages that have been paged out to the
 *      given device.  The corresponding blocks in the bitmap must be
 *      marked as allocated and the device must be flagged SW_CLOSING.
 *      There may be no processes swapped out to the device.
 *
 *      This routine may block.
 */
static void
swap_pager_swapoff(struct swdevt *sp)
{
        struct swblock *swap;
        int i, j, retries;

        GIANT_REQUIRED;

        retries = 0;
full_rescan:
        mtx_lock(&swhash_mtx);
        for (i = 0; i <= swhash_mask; i++) { /* '<=' is correct here */
restart:
                for (swap = swhash[i]; swap != NULL; swap = swap->swb_hnext) {
                        vm_object_t object = swap->swb_object;
                        vm_pindex_t pindex = swap->swb_index;
                        for (j = 0; j < SWAP_META_PAGES; ++j) {
                                if (swp_pager_isondev(swap->swb_pages[j], sp)) {
                                        /* avoid deadlock */
                                        if (!VM_OBJECT_TRYLOCK(object)) {
                                                break;
                                        } else {
                                                mtx_unlock(&swhash_mtx);
                                                swp_pager_force_pagein(object,
                                                    pindex + j);
                                                VM_OBJECT_UNLOCK(object);
                                                mtx_lock(&swhash_mtx);
                                                goto restart;
                                        }
                                }
                        }
                }
        }
        mtx_unlock(&swhash_mtx);
        if (sp->sw_used) {
                /*
                 * Objects may be locked or paging to the device being
                 * removed, so we will miss their pages and need to
                 * make another pass.  We have marked this device as
                 * SW_CLOSING, so the activity should finish soon.
                 */
                retries++;
                if (retries > 100) {
                        panic("swapoff: failed to locate %d swap blocks",
                            sp->sw_used);
                }
                pause("swpoff", hz / 20);
                goto full_rescan;
        }
}

/************************************************************************
 *                              SWAP META DATA                          *
 ************************************************************************
 *
 *      These routines manipulate the swap metadata stored in the 
 *      OBJT_SWAP object.  All swp_*() routines must be called at
 *      splvm() because swap can be freed up by the low level vm_page
 *      code which might be called from interrupts beyond what splbio() covers.
 *
 *      Swap metadata is implemented with a global hash and not directly
 *      linked into the object.  Instead the object simply contains
 *      appropriate tracking counters.
 */

/*
 * SWP_PAGER_META_BUILD() -     add swap block to swap meta data for object
 *
 *      We first convert the object to a swap object if it is a default
 *      object.
 *
 *      The specified swapblk is added to the object's swap metadata.  If
 *      the swapblk is not valid, it is freed instead.  Any previously
 *      assigned swapblk is freed.
 *
 *      This routine must be called at splvm(), except when used to convert
 *      an OBJT_DEFAULT object into an OBJT_SWAP object.
 */
static void
swp_pager_meta_build(vm_object_t object, vm_pindex_t pindex, daddr_t swapblk)
{
        struct swblock *swap;
        struct swblock **pswap;
        int idx;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        /*
         * Convert default object to swap object if necessary
         */
        if (object->type != OBJT_SWAP) {
                object->type = OBJT_SWAP;
                object->un_pager.swp.swp_bcount = 0;

                if (object->handle != NULL) {
                        mtx_lock(&sw_alloc_mtx);
                        TAILQ_INSERT_TAIL(
                            NOBJLIST(object->handle),
                            object, 
                            pager_object_list
                        );
                        mtx_unlock(&sw_alloc_mtx);
                }
        }
        
        /*
         * Locate hash entry.  If not found create, but if we aren't adding
         * anything just return.  If we run out of space in the map we wait
         * and, since the hash table may have changed, retry.
         */
retry:
        mtx_lock(&swhash_mtx);
        pswap = swp_pager_hash(object, pindex);

        if ((swap = *pswap) == NULL) {
                int i;

                if (swapblk == SWAPBLK_NONE)
                        goto done;

                swap = *pswap = uma_zalloc(swap_zone, M_NOWAIT);
                if (swap == NULL) {
                        mtx_unlock(&swhash_mtx);
                        VM_OBJECT_UNLOCK(object);
                        if (uma_zone_exhausted(swap_zone)) {
                                printf("swap zone exhausted, increase kern.maxswzone\n");
                                vm_pageout_oom(VM_OOM_SWAPZ);
                                pause("swzonex", 10);
                        } else
                                VM_WAIT;
                        VM_OBJECT_LOCK(object);
                        goto retry;
                }

                swap->swb_hnext = NULL;
                swap->swb_object = object;
                swap->swb_index = pindex & ~(vm_pindex_t)SWAP_META_MASK;
                swap->swb_count = 0;

                ++object->un_pager.swp.swp_bcount;

                for (i = 0; i < SWAP_META_PAGES; ++i)
                        swap->swb_pages[i] = SWAPBLK_NONE;
        }

        /*
         * Delete prior contents of metadata
         */
        idx = pindex & SWAP_META_MASK;

        if (swap->swb_pages[idx] != SWAPBLK_NONE) {
                swp_pager_freeswapspace(swap->swb_pages[idx], 1);
                --swap->swb_count;
        }

        /*
         * Enter block into metadata
         */
        swap->swb_pages[idx] = swapblk;
        if (swapblk != SWAPBLK_NONE)
                ++swap->swb_count;
done:
        mtx_unlock(&swhash_mtx);
}

/*
 * SWP_PAGER_META_FREE() - free a range of blocks in the object's swap metadata
 *
 *      The requested range of blocks is freed, with any associated swap 
 *      returned to the swap bitmap.
 *
 *      This routine will free swap metadata structures as they are cleaned 
 *      out.  This routine does *NOT* operate on swap metadata associated
 *      with resident pages.
 *
 *      This routine must be called at splvm()
 */
static void
swp_pager_meta_free(vm_object_t object, vm_pindex_t index, daddr_t count)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        if (object->type != OBJT_SWAP)
                return;

        while (count > 0) {
                struct swblock **pswap;
                struct swblock *swap;

                mtx_lock(&swhash_mtx);
                pswap = swp_pager_hash(object, index);

                if ((swap = *pswap) != NULL) {
                        daddr_t v = swap->swb_pages[index & SWAP_META_MASK];

                        if (v != SWAPBLK_NONE) {
                                swp_pager_freeswapspace(v, 1);
                                swap->swb_pages[index & SWAP_META_MASK] =
                                        SWAPBLK_NONE;
                                if (--swap->swb_count == 0) {
                                        *pswap = swap->swb_hnext;
                                        uma_zfree(swap_zone, swap);
                                        --object->un_pager.swp.swp_bcount;
                                }
                        }
                        --count;
                        ++index;
                } else {
                        int n = SWAP_META_PAGES - (index & SWAP_META_MASK);
                        count -= n;
                        index += n;
                }
                mtx_unlock(&swhash_mtx);
        }
}

/*
 * SWP_PAGER_META_FREE_ALL() - destroy all swap metadata associated with object
 *
 *      This routine locates and destroys all swap metadata associated with
 *      an object.
 *
 *      This routine must be called at splvm()
 */
static void
swp_pager_meta_free_all(vm_object_t object)
{
        daddr_t index = 0;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        if (object->type != OBJT_SWAP)
                return;

        while (object->un_pager.swp.swp_bcount) {
                struct swblock **pswap;
                struct swblock *swap;

                mtx_lock(&swhash_mtx);
                pswap = swp_pager_hash(object, index);
                if ((swap = *pswap) != NULL) {
                        int i;

                        for (i = 0; i < SWAP_META_PAGES; ++i) {
                                daddr_t v = swap->swb_pages[i];
                                if (v != SWAPBLK_NONE) {
                                        --swap->swb_count;
                                        swp_pager_freeswapspace(v, 1);
                                }
                        }
                        if (swap->swb_count != 0)
                                panic("swap_pager_meta_free_all: swb_count != 0");
                        *pswap = swap->swb_hnext;
                        uma_zfree(swap_zone, swap);
                        --object->un_pager.swp.swp_bcount;
                }
                mtx_unlock(&swhash_mtx);
                index += SWAP_META_PAGES;
                if (index > 0x20000000)
                        panic("swp_pager_meta_free_all: failed to locate all swap meta blocks");
        }
}

/*
 * SWP_PAGER_METACTL() -  misc control of swap and vm_page_t meta data.
 *
 *      This routine is capable of looking up, popping, or freeing
 *      swapblk assignments in the swap meta data or in the vm_page_t.
 *      The routine typically returns the swapblk being looked-up, or popped,
 *      or SWAPBLK_NONE if the block was freed, or SWAPBLK_NONE if the block
 *      was invalid.  This routine will automatically free any invalid 
 *      meta-data swapblks.
 *
 *      It is not possible to store invalid swapblks in the swap meta data
 *      (other then a literal 'SWAPBLK_NONE'), so we don't bother checking.
 *
 *      When acting on a busy resident page and paging is in progress, we 
 *      have to wait until paging is complete but otherwise can act on the 
 *      busy page.
 *
 *      This routine must be called at splvm().
 *
 *      SWM_FREE        remove and free swap block from metadata
 *      SWM_POP         remove from meta data but do not free.. pop it out
 */
static daddr_t
swp_pager_meta_ctl(vm_object_t object, vm_pindex_t pindex, int flags)
{
        struct swblock **pswap;
        struct swblock *swap;
        daddr_t r1;
        int idx;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        /*
         * The meta data only exists of the object is OBJT_SWAP 
         * and even then might not be allocated yet.
         */
        if (object->type != OBJT_SWAP)
                return (SWAPBLK_NONE);

        r1 = SWAPBLK_NONE;
        mtx_lock(&swhash_mtx);
        pswap = swp_pager_hash(object, pindex);

        if ((swap = *pswap) != NULL) {
                idx = pindex & SWAP_META_MASK;
                r1 = swap->swb_pages[idx];

                if (r1 != SWAPBLK_NONE) {
                        if (flags & SWM_FREE) {
                                swp_pager_freeswapspace(r1, 1);
                                r1 = SWAPBLK_NONE;
                        }
                        if (flags & (SWM_FREE|SWM_POP)) {
                                swap->swb_pages[idx] = SWAPBLK_NONE;
                                if (--swap->swb_count == 0) {
                                        *pswap = swap->swb_hnext;
                                        uma_zfree(swap_zone, swap);
                                        --object->un_pager.swp.swp_bcount;
                                }
                        } 
                }
        }
        mtx_unlock(&swhash_mtx);
        return (r1);
}

/*
 * System call swapon(name) enables swapping on device name,
 * which must be in the swdevsw.  Return EBUSY
 * if already swapping on this device.
 */
#ifndef _SYS_SYSPROTO_H_
struct swapon_args {
        char *name;
};
#endif

/* 
 * MPSAFE
 */
/* ARGSUSED */
int
swapon(struct thread *td, struct swapon_args *uap)
{
        struct vattr attr;
        struct vnode *vp;
        struct nameidata nd;
        int error;

        error = priv_check(td, PRIV_SWAPON);
        if (error)
                return (error);

        mtx_lock(&Giant);
        while (swdev_syscall_active)
            tsleep(&swdev_syscall_active, PUSER - 1, "swpon", 0);
        swdev_syscall_active = 1;

        /*
         * Swap metadata may not fit in the KVM if we have physical
         * memory of >1GB.
         */
        if (swap_zone == NULL) {
                error = ENOMEM;
                goto done;
        }

        NDINIT(&nd, LOOKUP, ISOPEN | FOLLOW | AUDITVNODE1, UIO_USERSPACE,
            uap->name, td);
        error = namei(&nd);
        if (error)
                goto done;

        NDFREE(&nd, NDF_ONLY_PNBUF);
        vp = nd.ni_vp;

        if (vn_isdisk(vp, &error)) {
                error = swapongeom(td, vp);
        } else if (vp->v_type == VREG &&
            (vp->v_mount->mnt_vfc->vfc_flags & VFCF_NETWORK) != 0 &&
            (error = VOP_GETATTR(vp, &attr, td->td_ucred)) == 0) {
                /*
                 * Allow direct swapping to NFS regular files in the same
                 * way that nfs_mountroot() sets up diskless swapping.
                 */
                error = swaponvp(td, vp, attr.va_size / DEV_BSIZE);
        }

        if (error)
                vrele(vp);
done:
        swdev_syscall_active = 0;
        wakeup_one(&swdev_syscall_active);
        mtx_unlock(&Giant);
        return (error);
}

static void
swaponsomething(struct vnode *vp, void *id, u_long nblks, sw_strategy_t *strategy, sw_close_t *close, dev_t dev)
{
        struct swdevt *sp, *tsp;
        swblk_t dvbase;
        u_long mblocks;

        /*
         * If we go beyond this, we get overflows in the radix
         * tree bitmap code.
         */
        mblocks = 0x40000000 / BLIST_META_RADIX;
        if (nblks > mblocks) {
                printf("WARNING: reducing size to maximum of %lu blocks per swap unit\n",
                        mblocks);
                nblks = mblocks;
        }
        /*
         * nblks is in DEV_BSIZE'd chunks, convert to PAGE_SIZE'd chunks.
         * First chop nblks off to page-align it, then convert.
         * 
         * sw->sw_nblks is in page-sized chunks now too.
         */
        nblks &= ~(ctodb(1) - 1);
        nblks = dbtoc(nblks);

        sp = malloc(sizeof *sp, M_VMPGDATA, M_WAITOK | M_ZERO);
        sp->sw_vp = vp;
        sp->sw_id = id;
        sp->sw_dev = dev;
        sp->sw_flags = 0;
        sp->sw_nblks = nblks;
        sp->sw_used = 0;
        sp->sw_strategy = strategy;
        sp->sw_close = close;

        sp->sw_blist = blist_create(nblks, M_WAITOK);
        /*
         * Do not free the first two block in order to avoid overwriting
         * any bsd label at the front of the partition
         */
        blist_free(sp->sw_blist, 2, nblks - 2);

        dvbase = 0;
        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(tsp, &swtailq, sw_list) {
                if (tsp->sw_end >= dvbase) {
                        /*
                         * We put one uncovered page between the devices
                         * in order to definitively prevent any cross-device
                         * I/O requests
                         */
                        dvbase = tsp->sw_end + 1;
                }
        }
        sp->sw_first = dvbase;
        sp->sw_end = dvbase + nblks;
        TAILQ_INSERT_TAIL(&swtailq, sp, sw_list);
        nswapdev++;
        swap_pager_avail += nblks;
        swap_total += (vm_ooffset_t)nblks * PAGE_SIZE;
        swp_sizecheck();
        mtx_unlock(&sw_dev_mtx);
}

/*
 * SYSCALL: swapoff(devname)
 *
 * Disable swapping on the given device.
 *
 * XXX: Badly designed system call: it should use a device index
 * rather than filename as specification.  We keep sw_vp around
 * only to make this work.
 */
#ifndef _SYS_SYSPROTO_H_
struct swapoff_args {
        char *name;
};
#endif

/*
 * MPSAFE
 */
/* ARGSUSED */
int
swapoff(struct thread *td, struct swapoff_args *uap)
{
        struct vnode *vp;
        struct nameidata nd;
        struct swdevt *sp;
        int error;

        error = priv_check(td, PRIV_SWAPOFF);
        if (error)
                return (error);

        mtx_lock(&Giant);
        while (swdev_syscall_active)
            tsleep(&swdev_syscall_active, PUSER - 1, "swpoff", 0);
        swdev_syscall_active = 1;

        NDINIT(&nd, LOOKUP, FOLLOW | AUDITVNODE1, UIO_USERSPACE, uap->name,
            td);
        error = namei(&nd);
        if (error)
                goto done;
        NDFREE(&nd, NDF_ONLY_PNBUF);
        vp = nd.ni_vp;

        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(sp, &swtailq, sw_list) {
                if (sp->sw_vp == vp)
                        break;
        }
        mtx_unlock(&sw_dev_mtx);
        if (sp == NULL) {
                error = EINVAL;
                goto done;
        }
        error = swapoff_one(sp, td->td_ucred);
done:
        swdev_syscall_active = 0;
        wakeup_one(&swdev_syscall_active);
        mtx_unlock(&Giant);
        return (error);
}

static int
swapoff_one(struct swdevt *sp, struct ucred *cred)
{
        u_long nblks, dvbase;
#ifdef MAC
        int error;
#endif

        mtx_assert(&Giant, MA_OWNED);
#ifdef MAC
        (void) vn_lock(sp->sw_vp, LK_EXCLUSIVE | LK_RETRY);
        error = mac_system_check_swapoff(cred, sp->sw_vp);
        (void) VOP_UNLOCK(sp->sw_vp, 0);
        if (error != 0)
                return (error);
#endif
        nblks = sp->sw_nblks;

        /*
         * We can turn off this swap device safely only if the
         * available virtual memory in the system will fit the amount
         * of data we will have to page back in, plus an epsilon so
         * the system doesn't become critically low on swap space.
         */
        if (cnt.v_free_count + cnt.v_cache_count + swap_pager_avail <
            nblks + nswap_lowat) {
                return (ENOMEM);
        }

        /*
         * Prevent further allocations on this device.
         */
        mtx_lock(&sw_dev_mtx);
        sp->sw_flags |= SW_CLOSING;
        for (dvbase = 0; dvbase < sp->sw_end; dvbase += dmmax) {
                swap_pager_avail -= blist_fill(sp->sw_blist,
                     dvbase, dmmax);
        }
        swap_total -= (vm_ooffset_t)nblks * PAGE_SIZE;
        mtx_unlock(&sw_dev_mtx);

        /*
         * Page in the contents of the device and close it.
         */
        swap_pager_swapoff(sp);

        sp->sw_close(curthread, sp);
        sp->sw_id = NULL;
        mtx_lock(&sw_dev_mtx);
        TAILQ_REMOVE(&swtailq, sp, sw_list);
        nswapdev--;
        if (nswapdev == 0) {
                swap_pager_full = 2;
                swap_pager_almost_full = 1;
        }
        if (swdevhd == sp)
                swdevhd = NULL;
        mtx_unlock(&sw_dev_mtx);
        blist_destroy(sp->sw_blist);
        free(sp, M_VMPGDATA);
        return (0);
}

void
swapoff_all(void)
{
        struct swdevt *sp, *spt;
        const char *devname;
        int error;
 
        mtx_lock(&Giant);
        while (swdev_syscall_active)
                tsleep(&swdev_syscall_active, PUSER - 1, "swpoff", 0);
        swdev_syscall_active = 1;
 
        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH_SAFE(sp, &swtailq, sw_list, spt) {
                mtx_unlock(&sw_dev_mtx);
                if (vn_isdisk(sp->sw_vp, NULL))
                        devname = sp->sw_vp->v_rdev->si_name;
                else
                        devname = "[file]";
                error = swapoff_one(sp, thread0.td_ucred);
                if (error != 0) {
                        printf("Cannot remove swap device %s (error=%d), "
                            "skipping.\n", devname, error);
                } else if (bootverbose) {
                        printf("Swap device %s removed.\n", devname);
                }
                mtx_lock(&sw_dev_mtx);
        }
        mtx_unlock(&sw_dev_mtx);
 
        swdev_syscall_active = 0;
        wakeup_one(&swdev_syscall_active);
        mtx_unlock(&Giant);
}

void
swap_pager_status(int *total, int *used)
{
        struct swdevt *sp;

        *total = 0;
        *used = 0;
        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(sp, &swtailq, sw_list) {
                *total += sp->sw_nblks;
                *used += sp->sw_used;
        }
        mtx_unlock(&sw_dev_mtx);
}

static int
sysctl_vm_swap_info(SYSCTL_HANDLER_ARGS)
{
        int     *name = (int *)arg1;
        int     error, n;
        struct xswdev xs;
        struct swdevt *sp;

        if (arg2 != 1) /* name length */
                return (EINVAL);

        n = 0;
        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(sp, &swtailq, sw_list) {
                if (n == *name) {
                        mtx_unlock(&sw_dev_mtx);
                        xs.xsw_version = XSWDEV_VERSION;
                        xs.xsw_dev = sp->sw_dev;
                        xs.xsw_flags = sp->sw_flags;
                        xs.xsw_nblks = sp->sw_nblks;
                        xs.xsw_used = sp->sw_used;

                        error = SYSCTL_OUT(req, &xs, sizeof(xs));
                        return (error);
                }
                n++;
        }
        mtx_unlock(&sw_dev_mtx);
        return (ENOENT);
}

SYSCTL_INT(_vm, OID_AUTO, nswapdev, CTLFLAG_RD, &nswapdev, 0,
    "Number of swap devices");
SYSCTL_NODE(_vm, OID_AUTO, swap_info, CTLFLAG_RD, sysctl_vm_swap_info,
    "Swap statistics by device");

/*
 * vmspace_swap_count() - count the approximate swap usage in pages for a
 *                        vmspace.
 *
 *      The map must be locked.
 *
 *      Swap usage is determined by taking the proportional swap used by
 *      VM objects backing the VM map.  To make up for fractional losses,
 *      if the VM object has any swap use at all the associated map entries
 *      count for at least 1 swap page.
 */
int
vmspace_swap_count(struct vmspace *vmspace)
{
        vm_map_t map = &vmspace->vm_map;
        vm_map_entry_t cur;
        int count = 0;

        for (cur = map->header.next; cur != &map->header; cur = cur->next) {
                vm_object_t object;

                if ((cur->eflags & MAP_ENTRY_IS_SUB_MAP) == 0 &&
                    (object = cur->object.vm_object) != NULL) {
                        VM_OBJECT_LOCK(object);
                        if (object->type == OBJT_SWAP &&
                            object->un_pager.swp.swp_bcount != 0) {
                                int n = (cur->end - cur->start) / PAGE_SIZE;

                                count += object->un_pager.swp.swp_bcount *
                                    SWAP_META_PAGES * n / object->size + 1;
                        }
                        VM_OBJECT_UNLOCK(object);
                }
        }
        return (count);
}

/*
 * GEOM backend
 *
 * Swapping onto disk devices.
 *
 */

static g_orphan_t swapgeom_orphan;

static struct g_class g_swap_class = {
        .name = "SWAP",
        .version = G_VERSION,
        .orphan = swapgeom_orphan,
};

DECLARE_GEOM_CLASS(g_swap_class, g_class);


static void
swapgeom_done(struct bio *bp2)
{
        struct buf *bp;

        bp = bp2->bio_caller2;
        bp->b_ioflags = bp2->bio_flags;
        if (bp2->bio_error)
                bp->b_ioflags |= BIO_ERROR;
        bp->b_resid = bp->b_bcount - bp2->bio_completed;
        bp->b_error = bp2->bio_error;
        bufdone(bp);
        g_destroy_bio(bp2);
}

static void
swapgeom_strategy(struct buf *bp, struct swdevt *sp)
{
        struct bio *bio;
        struct g_consumer *cp;

        cp = sp->sw_id;
        if (cp == NULL) {
                bp->b_error = ENXIO;
                bp->b_ioflags |= BIO_ERROR;
                bufdone(bp);
                return;
        }
        if (bp->b_iocmd == BIO_WRITE)
                bio = g_new_bio();
        else
                bio = g_alloc_bio();
        if (bio == NULL) {
                bp->b_error = ENOMEM;
                bp->b_ioflags |= BIO_ERROR;
                bufdone(bp);
                return;
        }

        bio->bio_caller2 = bp;
        bio->bio_cmd = bp->b_iocmd;
        bio->bio_data = bp->b_data;
        bio->bio_offset = (bp->b_blkno - sp->sw_first) * PAGE_SIZE;
        bio->bio_length = bp->b_bcount;
        bio->bio_done = swapgeom_done;
        g_io_request(bio, cp);
        return;
}

static void
swapgeom_orphan(struct g_consumer *cp)
{
        struct swdevt *sp;

        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(sp, &swtailq, sw_list)
                if (sp->sw_id == cp)
                        sp->sw_id = NULL;
        mtx_unlock(&sw_dev_mtx);
}

static void
swapgeom_close_ev(void *arg, int flags)
{
        struct g_consumer *cp;

        cp = arg;
        g_access(cp, -1, -1, 0);
        g_detach(cp);
        g_destroy_consumer(cp);
}

static void
swapgeom_close(struct thread *td, struct swdevt *sw)
{

        /* XXX: direct call when Giant untangled */
        g_waitfor_event(swapgeom_close_ev, sw->sw_id, M_WAITOK, NULL);
}


struct swh0h0 {
        struct cdev *dev;
        struct vnode *vp;
        int     error;
};

static void
swapongeom_ev(void *arg, int flags)
{
        struct swh0h0 *swh;
        struct g_provider *pp;
        struct g_consumer *cp;
        static struct g_geom *gp;
        struct swdevt *sp;
        u_long nblks;
        int error;

        swh = arg;
        swh->error = 0;
        pp = g_dev_getprovider(swh->dev);
        if (pp == NULL) {
                swh->error = ENODEV;
                return;
        }
        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(sp, &swtailq, sw_list) {
                cp = sp->sw_id;
                if (cp != NULL && cp->provider == pp) {
                        mtx_unlock(&sw_dev_mtx);
                        swh->error = EBUSY;
                        return;
                }
        }
        mtx_unlock(&sw_dev_mtx);
        if (gp == NULL)
                gp = g_new_geomf(&g_swap_class, "swap", NULL);
        cp = g_new_consumer(gp);
        g_attach(cp, pp);
        /*
         * XXX: Everytime you think you can improve the margin for
         * footshooting, somebody depends on the ability to do so:
         * savecore(8) wants to write to our swapdev so we cannot
         * set an exclusive count :-(
         */
        error = g_access(cp, 1, 1, 0);
        if (error) {
                g_detach(cp);
                g_destroy_consumer(cp);
                swh->error = error;
                return;
        }
        nblks = pp->mediasize / DEV_BSIZE;
        swaponsomething(swh->vp, cp, nblks, swapgeom_strategy,
            swapgeom_close, dev2udev(swh->dev));
        swh->error = 0;
        return;
}

static int
swapongeom(struct thread *td, struct vnode *vp)
{
        int error;
        struct swh0h0 swh;

        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);

        swh.dev = vp->v_rdev;
        swh.vp = vp;
        swh.error = 0;
        /* XXX: direct call when Giant untangled */
        error = g_waitfor_event(swapongeom_ev, &swh, M_WAITOK, NULL);
        if (!error)
                error = swh.error;
        VOP_UNLOCK(vp, 0);
        return (error);
}

/*
 * VNODE backend
 *
 * This is used mainly for network filesystem (read: probably only tested
 * with NFS) swapfiles.
 *
 */

static void
swapdev_strategy(struct buf *bp, struct swdevt *sp)
{
        struct vnode *vp2;

        bp->b_blkno = ctodb(bp->b_blkno - sp->sw_first);

        vp2 = sp->sw_id;
        vhold(vp2);
        if (bp->b_iocmd == BIO_WRITE) {
                if (bp->b_bufobj)
                        bufobj_wdrop(bp->b_bufobj);
                bufobj_wref(&vp2->v_bufobj);
        }
        if (bp->b_bufobj != &vp2->v_bufobj)
                bp->b_bufobj = &vp2->v_bufobj;
        bp->b_vp = vp2;
        bp->b_iooffset = dbtob(bp->b_blkno);
        bstrategy(bp);
        return;
}

static void
swapdev_close(struct thread *td, struct swdevt *sp)
{

        VOP_CLOSE(sp->sw_vp, FREAD | FWRITE, td->td_ucred, td);
        vrele(sp->sw_vp);
}


static int
swaponvp(struct thread *td, struct vnode *vp, u_long nblks)
{
        struct swdevt *sp;
        int error;

        if (nblks == 0)
                return (ENXIO);
        mtx_lock(&sw_dev_mtx);
        TAILQ_FOREACH(sp, &swtailq, sw_list) {
                if (sp->sw_id == vp) {
                        mtx_unlock(&sw_dev_mtx);
                        return (EBUSY);
                }
        }
        mtx_unlock(&sw_dev_mtx);
    
        (void) vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
#ifdef MAC
        error = mac_system_check_swapon(td->td_ucred, vp);
        if (error == 0)
#endif
                error = VOP_OPEN(vp, FREAD | FWRITE, td->td_ucred, td, NULL);
        (void) VOP_UNLOCK(vp, 0);
        if (error)
                return (error);

        swaponsomething(vp, vp, nblks, swapdev_strategy, swapdev_close,
            NODEV);
        return (0);
}